Medical electrodes have, in the past, taken many shapes and forms. Principally, they have been shaped according to the use for which they are intended. Electrodes used with monitoring apparatus, such as EKG and EEG machines, commonly have small round contact surfaces, whereas electrodes used with such stimulation apparatus as pain control devices tend to be larger and have rectangularly and other conveniently shaped contact surfaces. Whether intended for monitoring or stimulation use, a design objective for each electrode group has been, and continues to be, good electrical signal transmission between a patient's skin surface and the electrical cables connected to a particular piece of apparatus. With respect to stimulation and monitoring electrodes, efficient signal transmission across the epidermis conductor interface is desirable. Further, with respect to stimulation electrodes, effective signal transmission free of current concentration points or "hot spots" is also desirable.
Of the electrodes presently available, many offer combination structures including a metallic or otherwise conductive support member to which an electrical wire from an associated apparatus may be attached. In many instances, these electrodes need the addition of generous amounts of an electrode paste or gel applied directly to the conductive support member to enhance conductivity across the skin-electrode interface to the point where acceptable operating conditions are achieved. Other prior art electrodes teach the incorporation of an open cellular skin interface pad secured to a conductive support member. This pad as shown in U.S. Pat. No. 3,817,252, is often sponge material which functions to hold an amount of electrolyte solution in order to enhance conductivity across the skin-pad interface. Such an interface pad can be, alternately, saturated with electrode pastes or gels of the type that do run or evaporate as readily as electrolyte solutions.
None of these prior art electrodes offer satisfactory disposable structure, nor do they offer a structure which will maintain constant, efficient and effective electrical transmission for long periods of time without the need for additional electrode paste, gel or solution. Moreover, there is a tendency while using these electrodes, for the electrode gel to separate and/or to flow to a non-uniform thickness. Under these conditions, sections of the conductive support member could be exposed to the skin and local hot spots can result which can cause discomfort if not severe enough to cause burns to the patient's skin.
Prior art electrodes invariably must be secured to the surface of a patient's skin with medical adhesive tape or other securing medium. Very often an electrode secured in this manner will lift off from the skin because of perspiration and/or because of movement by the patient, creating a partial or total interruption in the signal transmission, or causing an uneven current density at the electrode-skin interface.
An objective of this invention, therefore, is to provide an electrode with an electroconductive skin-interface substrate, which will perform a similar function to, and eliminate the need for, an electrolyte solution, electrode paste or electrode gel.
Another objective of this invention is to provide an electrode with a skin-interface substrate having pressure sensitive adhesive properties which will enable the electrode to adhere to the skin without the use of tape or other securing mediums.
Another objective of this invention is to provide an adhesive substrate that has high tack so that minimal pressure is needed to apply it to the skin but is such that it can also be easily separable from the skin upon removal without any noticeable residue.
A further objective is to provide an electrode with a non-liquid skin-interface which is a film which will maintain a uniform thickness and will not separate to expose sections of a conductive support member to the skin.
An even further objective is to provide an electrode having a skin-interface substrate which will not decompose or dry out under long periods of use.